I'm not seeing any length limitations. As for does it require physical protection-(250.64(B) It would depend on the size of conductor, #8 needs to be in conduit, #6 can go in without conduit as long as it follows the surface of the building, #4 needs protection if subject to severe physical damage-(Hi-Lo type setting), and as to ty-wraping it to the feeder conduit. Someone has to make the call that it is "functionally associated" I'd make the call in my jurisdiction and probably say "No".
